Design of CNS-Li2SiO3 Permeable Protective Coatings and Effects on Mortar Matrix

Abstract

In this paper, we prepared permeable protective coatings composed of lithium silicate (Li2SiO3), where the coating was modified by colloidal nano-silica (CNS). Three levels of lithium silicate (i.e., 30 wt. %; 40 wt. %; 50 wt. %), sodium silicate (i.e., 5 wt. %; 10 wt. %; 15 wt. %), and surfactant (i.e., 0.05 wt. %; 0.1 wt. %; 0.15 wt. %) were involved in this study. An orthogonal experiment design selected the optimal proportion basedon thestrength and water absorption requirements of mortar. The effects of CNS-Li2SiO3 coating on the resistance to permeability of chloride ions and carbonation of specimens were also studied. The outcomes were interpreted using scanning electron microscopy (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) techniques. The results showed that the optimum mix formulation consisted of 40 wt. % of lithium silicate, 10 wt. % of sodium silicate and 0.1 wt. % of surfactant within the mixtures investigated. Meanwhile, compared tothe control group, after the specimens were coated at 21 days curing age of mortar, the strength development, 48-h water absorption, resistance to chloride ions penetration, and carbonation of CNS-Li2SiO3 coated specimenswere improved. This could be attributed to the second hydration, leading to a reduction of the content of Ca(OH)2 and an increase of the amount of C–S–H gel within specimens. Thus, the microstructure of mortar matrix was improved after coated with CNS-Li2SiO3 permeable protective coatings.